Conventionally, in an internal-combustion engine such as an automobile engine, a plasma ignition apparatus is proposed that supplies, for the expansion of a plasma region, a high frequency to a spark discharge as a core of the plasma to ignite an air-fuel mixture. Herein, the spark discharge is generated in a combustion chamber by using an ignition plug. This kind of plasma ignition apparatus includes a high frequency generating device that generates the high frequency (for example, Japanese Laid-open Patent Publication No. 2014-185544).
However, in the aforementioned conventional technology, for example, when a short circuit or the like occurs in a signal path to the high frequency generating device, the high frequency may be output at an unintended